1. Field of the invention
The present invention relates to a sheet feeding device incorporated in an image developing and processing machine such as a copy machine, a printing press or the like, and more particularly, relates to such a sheet feeding device for feeding sheets one by one to an image developing and processing section in the machine.
2. Prior art
The sheet feeding device incorporated in an image developing and processing device such as a copy machine, a printing press or the like is in general adapted to take up and feed a plurality of sheets one by one by means of a selectively driven sheet feeding roller from the stack thereof positioned on a sheet feeding base to a pair of register rollers or timing rollers and then to transport the sheet by the register rollers to an image developing and processing means such as a form cylinder or a copying photosensitive element drum at a timing that is in timed relation to the operation of the image developing and processing means. This type of sheet feeding devices are well known in the art and are shown and described for example in the Japanese Patent Publication No. 58-7582, the Japanese Patent Laying Open Publication No. 62-157145 and the like.
In such sheet feeding devices as mentioned above, each sheet fed by the sheet feeding roller from the sheet feeding base toward the image developing and processing means once stops with its leading edge contacting with the register rollers at the contact parts therebetween, and is transported at a predetermined timing to the image developing and processing means by the register rollers which are started to rotate at a predetermined timing. Since the sheet feeding roller continues to rotate at least for a little while even after a sheet has arrived at and contacted with the register rollers at the leading edge thereof, the sheet generates in itself a ridge-like curvature growing across the moving direction thereof between the sheet feeding roller and the register rollers before the latter rollers begin to transport the sheet towards the image developing and processing means.
In order to permit such a sheet deformation as mentioned above, therefore, a sheet guide passage defined between the sheet feeding roller and the register rollers must have a relatively large space extended in the direction of the curvature growth and, accordingly, an upper guide plate which defines the upper boundary of the sheet guide passage is in general bent upward at the front part thereof to extend the upper space of the passage.
With the sheet guide passage being constructed as above, if the leading end of the sheet being fed through the passage has been curled up, it comes into collision against the upwardly bent portion of the upper guide plate and is prevented from moving further, resulting in an abnormal sheet feeding and causing a sheet jamming. Especially, if such a situation occurred when a relatively tough sheet such as a cardboard or the like being used, it could not be fed further because of the jamming.
On the other hand, if the inclination of the upwardly bent portion of the upper guide plate was reduced and the extended upper space in the sheet guide passage was reduced, the drawback mentioned Just above might be eliminated. In that event, however, sheet would be impeded from generating a necessary arcuate deformation, resulting in improper sheet feeding.